The present invention relates to automatic molded case industrial circuit breakers and particularly to such circuit breakers having static or solid state trip units instead of the traditional thermal-magnetic trip units.
Electronic solid state trip units are increasingly being implemented in industrial circuit breakers in place of the traditional thermal and magnetic trip units to initiate circuit interruption automatically in response to an abnormal current condition in a protected load circuit. The increasing popularity of static trip units is largely due to their inherent versatility and rather precise repeatability of selected trip-time response characteristics. That is, a circuit breaker static trip unit can be designed to accommodate a wide range of user selected response characteristics calculated to establish a highly repeatable trip-time curve rather precisely tailored to a particular load so as to afford a full measure of overcurrent protection ranging from light overload to heavy short circuit proportions. Another attractive aspect of static trip units is that they can be readily and economically supplemented to also afford ground fault protection for a load circuit. In fact, the extreme versatility of modern static trip units presents a potential customer for an industrial circuit breaker with numerous options, i.e., functions, analogous to what one faces when buying a new automobile.
It is accordingly an object of the present invention to provide an improved static trip unit for industrial molded case circuit breakers.
A further object is to provide a static trip unit of compact size capable of being incorporated in a circuit breaker molded case of the same envelope size as one incorporating a traditional thermal and/or magnetic trip unit.
Yet another object is to provide a static trip unit of the above character having readily interchangeable modular parts to facilitate the accommodation of customer needs in terms of options or functions.
An additional object is to provide a static trip unit of the above character wherein the interchangeability of modules facilitates field servicing and accommodates the addition of options to increase the capabilities of circuit breakers already in the field.
Still another object is to provide a static trip unit of the above character which is efficient in construction, convenient to fabricate and assemble, and readily integrable into a molded case industrial circuit breaker, both in the factory and in the field.
Other objects of the invention will in part be obvious and in part appear hereinafter.